The present invention generally relates to a full-size optical sensor device, and more particularly to a full-size optical sensor which is applied to a contact type full-size image sensor used in a document scanner, a liquid crystal display, an EL display and so on.
Conventionally, a contact type full-size optical image sensor is, for example, used as an image sensor for reading an image from a document. The contact type full-size image sensor has substantially the same width as the document and is used so as to be substantially in contact with the document. Thus, it is unnecessary to provide a reducing optical system for the contact type full-size image sensor so as to prevent the image sensor from becoming large. The contact type full-size image sensor described above is basically structured as in FIG. 1. Referring to FIG. 1, a plurality of photoelectric conversion elements Sl through Sn are arranged in a line. The plurality of photoelectric conversion elements Sl through Sn make up a sensor array 1. Each of the plurality of photoelectric conversion elements Sl through Sn is made up of a photo diode and a capacitance. An end of each of the plurality of photoelectric conversion elements Sl through Sn is connected to a corresponding one of bits Bl through Bn of a shift register 2. The other end of each of photoelectric conversion elements Sl through Sn is connected to a signal output line 3. Then, each of the photoelectric conversion elements Sl through Sn is driven by a corresponding one of the bits Bl through Bn of the shift register 2, and an electrical signal generated by each of the photoelectric conversion elements Sl through Sn is supplied through the signal output line 3 to a process system including a peak hold circuit and so on. In this contact type full-size image sensor, the photoelectric conversion elements Sl through Sn are formed on a substrate as the sensor array 1, and the shift register 2, which operates as a driver circuit made up of thin film transistors, is also formed on the substrate.
It has been proposed that, to increase the number of photoelectric conversion elements within a predetermined length, which is termed a density of elements, a density of the sensor array or the like, the thin film transistor (TFT) in the driver circuit be miniaturized. However, for example, in a case where the driver circuit is formed on a substrate having a large square measurement such as 30 cm .times.30 cm, the elasticizing of the substrate during the production, namely the deformation of the substrate which is generated due to an increase and a decrease in the temperature which occurs during the production process of the image sensor, is relatively large. Thus, in this case, it is difficult to miniaturize the TFT. In the contact type full-size image sensor having the structure as shown in FIG. 1, when the density of the sensor array 1 is doubled, the number of TFTs making up the shift register, which is termed as the density of TFTs, the density of the shift register or the like, must also be doubled. However, it is difficult to increase the density of TFTs due to the above mentioned deformation of the substrate.
For example, in the conventional image sensor in which the density of the shift register is a value of 16 dot/ mm, the length of each 1-bit of the shift register in the main scanning direction of the image sensor is 62.5 .mu.m. In a case where the image sensor having the high density as has been described above is produced in accordance with the conventional production process, a mask alignment error, an alignment error at the time of the photolithography process and so on does occur. Thus, the output signal from the conventional high density image sensor is distorted in comparison with the sensor having a low density such as 8 dot/mm
To eliminate the disadvantages described above and to increase the density of the sensor array, it is necessary to provide a circuit in which a 1-bit of the shift register can drive a plurality of photoelectric conversion elements. More particularly, it is necessary to provide signal synchronous circuits so as to respectively control the output from each corresponding 1-bit of the shift register and to select from each corresponding plurality of photoelectric conversion elements one of the photoelectric conversion elements.
From this view point, a full-size image sensor having a plurality of the shift registers is disclosed in Japanese Laid-Open Patent Application No. 61-39570. FIG. 2 generally indicates this type of full-size image sensor. Referring to FIG. 2, an end of each photoelectric conversion element Sl through Sn in a sensor array 5 is connected to a signal output line 4. The other end of each of photoelectric conversion elements Sl through Sn is connected to a corresponding analogue switch 6. Each of analogue switches 6 is formed of the TFT. The analogue switches 6 are divided into a plurality of groups. Each of the groups includes n analogue switches 6. Due to two registers 7 and 8 and a matrix line circuit g, the groups are successively selected and the analogue switches 6 in each of the groups are successively driven.
Another full-size image sensor is disclosed in Japanese Laid-Open Patent Application No.60-218870. For example, FIG. 3 indicates this type of full-size image sensor. Referring to FIG. 3, a plurality of photoelectric conversion elements of the sensor array 10 are divided into a plurality of groups. Each of the groups includes n photoelectric conversion elements. Common electrodes of all photoelectric conversion elements in each of the groups are commonly connected to one of the bits Bl through Bn of the shift register 11. Independent electrodes of the photoelectric conversion elements positioned at the same order i (i=1, 2, . . . and n ) in every group are connected with each other by a matrix line circuit 12, and then output signals from each of the photoelectric conversion elements are supplied through the matrix line circuit 12 to the processing system.
In the full-size image sensor having the matrix circuitry line as has been described above, unwanted capacities are generated in parts of the matrix circuit line where lines in the matrix circuitry line are crossed with each other so that periodical noises occur.
In the former Japanese Laid-Open Patent Application which has the plurality of the shift registers, output lines of each of the shift registers are long so that the output from each of the shift register is attenuated, and thus a dispersion among the levels of output signals corresponding to the bits of the image sensor occurs.
In the later one, the plurality of output signal lines are provided so that it is necessary to provide a processing circuit coupled to each of the output signal lines, and thus the processing system is generally complicated.